1. Field of the Invention
The present invention relates to a nuclear reactor core arrangement. More particularly, this invention relates to a nuclear reactor core arrangement which is adapted to combust plutonium along with uranium fuels and which utilizes a plurality of fuel assemblies that include mixed-oxide (MOX) fuel rods.
2. Discussion of the Related Art
The Department of Energy (DOE) has a large excess of plutonium resulting from the retirement of nuclear weapons and is considering options for its disposal. One option recommended by the National Academy of Sciences (NAS) for the disposal of the excess weapons-grade plutonium is conversion to spent fuel. In this approach, the excess weapons plutonium is converted to plutonium oxide (PuO.sub.2) and used in a mixed oxide (PuO.sub.2 --UO.sub.2) form without reprocessing as fuel for existing nuclear reactors. This results in a spent fuel form which is "proliferation resistant" and that meets the "spent fuel standard" which is recommended by the NAS and which is being used by the DOE.
However, this mixed oxide (MOX) approach requires: 1) conservative, realistic core performance characteristics which are similar to those for current uranium core designs; 2) that the technique minimize licensing risks by avoiding any erosion of safety margins compared to those for currently licensed conventional uranium core designs; 3) that impacts on plant operation be minimized or totally avoided; and 4) that the energy extracted from the MOX fuel be maximized, thus providing the best economics.
Accordingly, ground rules were established by the DOE in light of the above objective. Namely, it is required that:
There is no mixing of MOX and burnable absorber in the same fuel rod. This allows manufacture of lead test assemblies in existing European MOX fuel fabrication facilities. PA1 The fuel and core designs are developed using existing fuel and core design methodologies. PA1 The equilibrium cycle core design characteristics using MOX matches current uranium oxide (UO.sub.2) reload core design characteristics as much as possible. PA1 The cycle length of the MOX core design is essentially the same as that of the UO.sub.2 core design. PA1 There is no significant (if any) plant modifications necessary. PA1 There is no significant impact on plant systems or operation. PA1 Plant parameters should remain within existing plant technical specifications to the greatest extent possible.
Accordingly, there exists a need for a nuclear core arrangement which can used in existing facilities and which enables an acceptably high throughput of plutonium in the form of MOX, while remaining within the above constraints.